As a cutting process for a workpiece is performed by means of a cutting tool to which cutting inserts are mounted, a corner cutting edge of the cutting insert is worn away. For example, in a process of cutting the workpiece by a milling machine, a corner cutting edge of the cutting insert mounted to a cutter is worn away, and so the cutting insert having a worn corner cutting edge can not cut precisely the workpiece.
Thus, the user needs to replace periodically the cutting insert having a worn corner cutting edge with new one. However, it is not economically preferable to remove an expensive cutting insert having one worn corner cutting edge and mount new cutting insert to the cutter.
To extend the service life time of the cutting insert, a cutting insert on which a plurality of corner cutting edges are formed are in need. However, it is extremely difficult to form a plurality of corner cutting edges on a small-sized cutting insert to be mounted to a small-sized cutter, for example, a small-sized cutter having a diameter (φ) of 16 to 40 mm.
In addition, it is difficult to form a clamping hole with a large diameter on the small-sized cutting insert and to form sufficient mounting surface on the small-sized cutting insert for stable mounting the cutting insert a pocket of the cutter.